JP2002208155A - Optical disc tilt correction method and optical disc apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device for searching a tilt correction amount with high accuracy and at a high speed. SOLUTION: By simultaneously searching optimal tilt driving values in two directions, the effect of the tilt driving value of each direction to a searching result is eliminated, the necessity of repeating the searching of the tilt driving values is eliminated, and two-direction tilting correction is achieved with high accuracy and at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for optically recording a signal on a record carrier using a light source such as a laser or reproducing the recorded signal, and more particularly to a method for correcting the tilt of an optical disk and The present invention relates to an optical disk device.

[0002]

2. Description of the Related Art As an example of tilt correction in a conventional optical disk device, a tilt control target position is corrected so as to minimize jitter as disclosed in Japanese Patent Application Laid-Open No. 8-293126 (tilt control device). It has been known. FIG. 11 is a block diagram showing a schematic configuration of a conventional optical disk device. The optical pickup 111 has a laser light emitting element, a converging lens, and an actuator, and irradiates the converged light beam 112 onto the optical disc 101. The optical pickup 111 further has a light receiving element, receives a light beam reflected on the information recording surface of the optical disk 101 and enters the light receiving element, and binarizes an RF signal corresponding to information recorded on the optical disk 101. Output to the circuit 121.

[0003] A binarization circuit 121 binarizes an RF signal at an appropriate slice level. The binarized signal is input to the jitter detection circuit 122, and the jitter detection circuit 122
DSP that detects the jitter of the binarized signal and uses it as a jitter signal
(Digital signal processor) 130. D
The SP 130 controls the level of the jitter signal using the built-in AD converter 1.
35. In the following description,
The level of the jitter signal detected inside the DSP 130 is called a jitter value.

The tilt sensor 142 detects the angle between the normal line of the information recording surface of the optical disc 101 and the optical axis of the light beam 112, and outputs a tilt signal corresponding to the detected angle to the tilt control circuit 143. The tilt control circuit 143 outputs a tilt drive signal to the tilt mechanism 141 based on the input tilt signal and a tilt control target signal input from the DSP 130 described later. The tilt mechanism 141 changes the angle of the optical pickup 111 with respect to the optical disc 101 according to a tilt drive signal input from the tilt control circuit 143. In this manner, the tilt control for controlling the angle between the normal line of the information recording surface of the optical disc 101 and the optical axis of the light beam 112 to a desired value is configured and operated.

[0005] The DSP 130 outputs a tilt control target signal corresponding to the above-described tilt control target to the tilt control circuit 143 from the built-in DA converter 138. The tilt control circuit 143 performs tilt control so that the input tilt control target signal and the tilt signal match. In the following description, D
The value before the DA conversion of the tilt control target signal inside the SP 130 is referred to as a tilt control target value.

Next, a procedure for searching for an optimum tilt control target in the above configuration will be described. The tilt detection signal measuring unit 131, which is a function implemented by the program of the DSP 130, sets a predetermined tilt control target value to the DSP 1
The tilt control target 143 is output to the tilt control circuit 143 as a tilt control target signal by the D / A converter 138 built in, and the tilt control target is changed. The jitter signal is captured by the AD converter 135, and the tilt control target value and the jitter value at that time are obtained. DSP
130 is stored in a built-in memory 132. The tilt detection signal measuring section 131 changes the tilt control target value over a predetermined range and repeats the above measurement operation.

The optimum tilt correction amount searching unit 133, which is a function realized by the program of the DSP 130, has a minimum jitter value based on the relationship between the tilt control target value and the jitter value measured by the tilt detection signal measuring unit 131 and stored in the memory 132. Is obtained as an optimum value, and a tilt control target signal corresponding to the tilt control target value is output to the tilt control circuit 143. With the above operation procedure, the tilt control circuit 143 performs the tilt control with the control target at which the jitter signal is minimized.

[0008]

In the prior art, for example, when searching for an optimum tilt control target in two directions, a radial direction (radial) and a circumferential direction (tangential) of the disk, the tilt mechanism 141 is used. A configuration corresponding to tilt correction in two directions is performed, and a search for a tilt control target value that minimizes the jitter value is performed in each of the radial and tangential directions in the same manner as the above procedure. However, this method has a problem as described below.

FIG. 9A shows the characteristic of the jitter value with respect to the tilt control target value in two directions of radial and tangential by the contour line of the jitter value. The horizontal axis is the radial tilt control target value, and the vertical axis is the vertical axis. Represents a tangential tilt control target value, and point O represents a point which is an optimal two-way tilt control target value at which the jitter value is minimized. FIG. 9B
9A is a characteristic of the jitter value with respect to the radial tilt control target value in a state where the tangential tilt control target value with respect to the characteristic of FIG. 9A is T10 and T11. Here, the tangential tilt control target value is T
In the case of deviation from the optimum tilt control target value T11 at 10, the jitter value with respect to the change Δr of the tilt control target value at the radial tilt control target value R10 at which the jitter value becomes the minimum as shown in FIG. Change Δj becomes smaller. That is, since the sensitivity of the jitter value to the radial tilt control target value is reduced, there is a problem in that the search accuracy of the tilt control target value that minimizes the jitter value is deteriorated.

FIG. 10A shows the characteristic of the jitter value with respect to the tilt control target values in the two directions of radial and tangential by contour lines of the jitter value. The horizontal axis indicates the radial tilt control target value, and the vertical axis indicates the vertical tilt control target value. The axis indicates the tangential tilt control target value, and the point O indicates the point which is the optimum two-way tilt control target value at which the jitter value is minimized. FIG.
10B shows the characteristic of the jitter value with respect to the radial tilt control target value when the tangential tilt control target values for the characteristic of FIG. 10A are T20 and T21. Here, when the tangential tilt control target value deviates from the optimum tilt control target value T21 at T20, as shown in FIG. 10B, the tilt control target value at which the radial jitter value becomes minimum is obtained. R20
And deviates from the optimum radial tilt control target value R21.

Therefore, in the search in which the jitter value in one direction is minimum, the point A in FIG. 10A where the tilt control target value in two directions is shifted from the point O where the jitter value is minimum before the search. In this case, first, a radial tilt control target value is searched for point B, then a tangential tilt control target value is searched for point C, and then a radial tilt control target value is searched for point D,. Thus, it is necessary to repeat the search for the tilt control target value for each of the radial and the tangential alternately. For this reason, the optimal 2 that minimizes the jitter value
There is a problem that the time for searching for the tilt control target value in the direction increases.

In order to solve the above problem, the present invention measures a tilt detection signal for a tilt correction amount in two directions, and comprises a tilt correction amount in two directions and a jitter value.
It is an object of the present invention to provide an optical disc apparatus that searches for a tilt correction amount at high speed and with high accuracy by obtaining an optimum tilt correction amount in two directions from characteristics in a dimensional space.

[0013]

In order to solve this problem, the present invention provides a tilt error which varies according to a tilt angle in two directions generated between an information recording surface of a record carrier and an optical axis of a light beam. Generating a signal, changing the tilt angle in two directions generated between the information recording surface of the record carrier and the optical axis of the light beam,
An optical disc tilt correction method characterized by searching for and determining an optimum correction amount based on characteristics in a three-dimensional space constituted by a tilt error signal and a correction amount for a tilt angle in two directions.

The present invention also relates to an apparatus for optically recording and reproducing information on and from a record carrier, the apparatus being adapted to respond to two tilt angles occurring between the information recording surface of the record carrier and the optical axis of the light beam. Tilt error signal generating means for generating a signal which varies according to the tilt angle, tilt correcting means for correcting a tilt angle in two directions generated between the information recording surface of the record carrier and the optical axis of the light beam, and the tilt error signal generating means An optical disc having an optimum tilt correction amount searching means for searching for and determining an optimum correction amount based on a characteristic in a three-dimensional space composed of a signal of the two directions and a correction amount for a tilt angle in two directions for driving the tilt correcting means. Device.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk apparatus according to the present invention will be described with reference to FIG. 1 which is a block diagram showing the configuration. In the following description, the same components as those of the related art are denoted by the same reference numerals, and description thereof will be omitted.

The DSP 130 outputs a two-way radial and tangential tilt drive signal from the built-in DA converter 1381 to the tilt mechanism 1411 based on the jitter value corresponding to the jitter signal level detected by the built-in AD converter 135. I do. The tilt mechanism 1411 changes the angle in two directions (the angle in the radial direction and the angle in the tangential direction) between the information recording surface of the optical disc 101 and the optical axis of the light beam 112 based on the input two-way tilt drive signals. The DSP 130 outputs a two-way tilt drive signal that minimizes the jitter value, and operates the tilt mechanism 1411 so that the angle between the information recording surface of the optical disk 101 and the optical axis of the light beam 112 is minimized. Let it.

In the following description, a value before the DA conversion of the tilt drive signal inside the DSP 130 is referred to as a tilt drive value. A tilt drive value that minimizes a jitter value at which a reproduction signal with the highest quality is obtained is referred to as an optimum tilt drive value.

The operation of the embodiment will be described below with reference to the flowchart of FIG. In the following description, FIG.
In the description corresponding to each step of the flowchart of FIG. 2, the numbers described in the flowchart of FIG. DSP
The tilt detection signal measuring unit 1311, which is a function realized by the program 130, converts a predetermined two-way tilt drive value into a digital signal by the DA converter 1381 built in the DSP 130.
A tilt drive signal is output to the tilt mechanism 1411 as a tilt drive signal in the direction (S101), and the level of the jitter signal is fetched as a jitter value by the AD converter 135 (S102).
It is stored in the built-in memory 132 (S103).

The tilt detection signal measuring unit 1311 repeats the above-described measurement operation over two predetermined ranges of tilt drive values over a predetermined range, and comprises a tilt drive value and a jitter value in two directions as shown in FIG. The characteristic in the three-dimensional space to be measured is measured (S104). FIG. 3A is a diagram showing a three-dimensional space composed of radial and tangential tilt drive values and jitter values. Each intersection of the mesh display is shown in two directions measured by the tilt detection signal measuring unit 1311. Are points indicating the measured values of the jitter values for the tilt drive value measurement points, and point O31 of these points is the point at which the jitter value is minimized. FIG. 3A shows the characteristic when the measurement of the jitter value at a total of 25 points is repeated at 5 points for each of the tilt drive values in two directions within a predetermined range.

The optimum tilt drive value search unit 1331, which is a function realized by the program of the DSP 130, calculates the jitter value from the two-direction tilt drive value and the jitter value measured by the tilt detection signal measurement unit 1311 and stored in the memory 132. A search is made for a minimum two-way tilt drive value (S10).
5). A two-way tilt drive signal corresponding to the searched two-way tilt drive value is output to the tilt mechanism 1411 (S
106).

Next, a method of searching for a tilt drive value at which the jitter value becomes minimum in S105 of FIG. 2 will be described in detail. The optimum tilt drive value search unit 1331 is provided in the memory 13
2, a tilt drive value in the two directions that minimizes the jitter value is searched from the two sets of the tilt drive values and the jitter values in the two directions, and the tilt drive values in the two directions are extracted as the optimum tilt drive values. decide. That is, the measured values of the jitter values in FIG. 3A are compared with each other, and the tilt drive value in the two directions of the point O31 which is the minimum among all the measured values is determined as the optimum tilt drive value.

According to the method described above, the tilt drive value in the two directions is changed even if the tilt drive value before searching for the tilt drive value in the two directions that minimizes the jitter value deviates from the optimum tilt drive value. Thus, a tilt drive value in two directions that minimizes the jitter value can be searched for.

Further, in the search for the tilt drive value at which the jitter value is minimized in S105 of FIG. 2, the optimum tilt drive value is searched with higher accuracy than the steps of the tilt drive values in two directions measured by the tilt detection signal measuring unit 1311. There is a method of searching for an optimum tilt drive value using a function approximation as described below. Optimal tilt drive value search unit 133
1 approximates the characteristic of the jitter value with respect to the two-way tilt drive value stored in the memory 132 to a binary function, calculates the two-way tilt drive value that minimizes the jitter value of the approximated function, and calculates it. It is determined as the optimum tilt drive value.

More specifically, an approximate function is expressed by the following (Equation 1) where the jitter value is a polynomial of the tilt drive value in two directions, r and t are the tilt drive values in two directions, and j is the jitter value. Function. However, k1 to k6 are arbitrary constants.

[0025]

(Equation 1)

Here, the constants of k1 to k6 in (Equation 1) are as follows:
Of the combinations of the tilt drive values and the jitter values in the two directions stored in the memory 132, six arbitrary combinations are substituted into (Equation 1), and the equations are obtained by solving a six-dimensional linear simultaneous equation for k1 to k6. . The function obtained here becomes a characteristic in a three-dimensional space composed of a tilt drive value in two directions and a jitter value as shown by a lattice-like curved surface in FIG.
The tilt drive value in the two directions of the point O32 where the jitter value becomes minimum with higher accuracy than the measurement point step in FIG.

That is, (Equation 1) is a quadratic function for each of r and t, and the condition for minimizing the jitter value j is obtained by partially differentiating the left side of (Equation 1) for each of r and t. The condition that the expression becomes 0, that is, the following (Equation 2)
And (Equation 3) are satisfied.

[0028]

(Equation 2)

[0029]

(Equation 3)

Here, when (Equation 2) and (Equation 3) are solved for r and t, the following (Equation 4) and (Equation 5) are obtained.

[0031]

(Equation 4)

[0032]

(Equation 5)

The tilt drive value in two directions that minimizes the jitter is calculated by substituting k1 to k5 into (Equation 4) and (Equation 5).

Further, a description will be given of a method of calculating coefficients k1 to k6 of the function of (Equation 1) by the least squares method using singular value decomposition. By using this method, it is possible to obtain the optimum tilt drive value in two directions with high accuracy from the function calculated by the least squares method, as compared with the method of solving the above-described six-dimensional linear simultaneous equations. In the above-described method, the coefficient of (Equation 1) is obtained from the combinations of the six sets of the tilt drive values in two directions and the jitter value. In the method described below, the coefficient of (Equation 1) is obtained from the combination of six or more sets. Determined by the least squares method. First, (Equation 1)
Into n sets of tilt drive values and jitter values in two directions stored in the memory 132 (n is a natural number of 6 or more)
Then, it is considered as a 6-element linear simultaneous equation for k1 to k6 expressed as the following (Equation 6).

[0035]

(Equation 6)

A determinant is considered using n sets of tilt drive values r1 to rn and t1 to tn and jitter values j1 to jn in two directions stored in the memory 132. For a matrix K of 6 rows and 1 column in which constants k1 to k6 in (Equation 6) are elements of columns,

[0037]

(Equation 7)

The n sets of tilt drive values r1 to rn and t1 to tn in the two directions stored in the memory 132 are substituted into (Equation 6), and the coefficients for k1 to k6 in (Equation 6) are calculated. Matrix of n rows and 6 columns configured as elements of

[0039]

(Equation 8)

A matrix J of n rows and 1 column using n pieces of jitter values j1 to jn stored in the memory 132 as column elements

[0041]

(Equation 9)

Then, the simultaneous equation of (Equation 6) is expressed by the following (Equation 10).

[0043]

(Equation 10)

Here, U is a column orthogonal matrix of n rows and 6 columns, and w is 6
A matrix A is represented by the following (Equation 11) by singular value decomposition, where a row 6 column diagonal matrix and V is a 6 row 6 column orthogonal matrix.
Singular value decomposition is generally known to those skilled in the art, and is described in detail in "NUMERICAL RECI
PES in C '' (William H. Press etl., Cambrid G7 Univer
sity Press, 1988), and the description in this embodiment is omitted.

[0045]

[Equation 11]

From (Equation 10) and (Equation 11), the following (Equation 1)
2) is derived. Using this (Equation 12), the matrix K is calculated from the matrices U and V obtained by singular value decomposition of the matrix A, the singular value matrix w, and the jitter value matrix J.

[0047]

(Equation 12)

Here, the matrix K calculated by (Equation 12) is a least-squares solution of the simultaneous equations (Equation 10). By substituting the elements k1 to k6 of this matrix K into (Equation 1), the minimum An approximate function for the jitter value j with respect to the tilt drive values r and t in two directions using the coefficients calculated by the multiplication method is obtained. By substituting the obtained coefficients k1 to k5 of the approximation function into (Equation 4) and (Equation 5), a two-way tilt drive value that minimizes the jitter value in the approximation function is obtained. I do. With the method described above,
By using the approximation function obtained by the least-squares method, it is possible to search for a tilt drive value in two directions that minimizes the jitter value with high accuracy.

Further, a method of omitting the above-described calculation of the singular value decomposition will be described below. A combination of two-direction tilt drive values for measuring the jitter value in the tilt detection signal measurement unit 1311 is determined in advance, and the determined two-direction tilt drive values r1 to rn and t1 to tn are used (Equation 8). The matrix A calculated is invariant. A matrix U obtained by subjecting the matrix A to singular value decomposition represented by (Equation 11),
w and V are also invariant, and the matrices U, w and V calculated in advance are
It is stored in the memory 132 built in the SP 130. Complicated by configuring the optimum tilt search unit 1331 so as to obtain an approximate function from the stored matrices U, w, and V and the jitter value measured in step 103 and stored in the memory 132 using (Equation 12) It is not necessary to calculate a singular value decomposition.

The method described above greatly reduces the complicated function approximation by the least-squares method, and further reduces the effect of the jitter value measurement error by using the least-squares method. The search for the driving value can be realized with high accuracy.

Next, a description will be given of a method for further improving the method of searching for the optimum tilt drive value in the embodiment. FIG. 4 and FIG. 5 are diagrams in which characteristics in a three-dimensional space composed of radial and tangential tilt drive values and jitter values are represented by grid-like curved surfaces. Point O in FIG.
4. The point O5 in FIG. 5 is a point where the jitter value in the characteristic represented by the lattice-shaped curved surface is minimum, and the concentric lines surrounding the point where the jitter value is minimum are contour lines indicating the same jitter value. is there. The portions surrounded by the dotted lines in the characteristics represented by the lattice-like curved surfaces in FIGS. 4 and 5 indicate smooth portions where the jitter value is almost constant and does not change.

FIG. 4 shows a characteristic in which the point where the jitter value becomes minimum is located substantially at the center of the smooth portion, and FIG. 5 shows a characteristic in which the point where the jitter value becomes minimum is shifted from the center of the smooth portion. . First, consider the case of a pot-like characteristic having a smooth portion surrounded by a dotted line in FIG. Since the jitter value is almost constant and does not change in the smoothed portion, the tilt detection signal measuring unit 13
The measurement error in the measurement of the jitter value according to 11 cannot be ignored compared to the change in the jitter value in the smooth portion. At this time, when the jitter value near the boundary of the smooth portion is measured and the optimum tilt drive value search unit 1331 searches for the tilt drive value in two directions at which the jitter value is minimized, the vicinity of the boundary of the smooth portion is determined as the optimum tilt drive value. Would.

Also, as shown in FIG. 5, when the characteristic is such that the drive value in the two directions at which the jitter value is minimum is located at the point O5 which is deviated from the smooth portion, the optimum tilt drive value search unit 1331
Searches for a tilt drive value in two directions that minimizes the jitter value, and determines the point O5 as the optimum tilt drive value. In such a case, the vicinity of the boundary of the smooth portion is determined as the optimum tilt drive value, and the tilt mechanism 1411 is operated by a tilt drive signal corresponding to the tilt drive value. The disadvantages at this time will be described.

FIG. 6A shows a range of a smooth portion on a curved surface having the above-described three-dimensional characteristic with respect to the radial and tangential tilt drive values. A point O60 is a point near the center of the smooth portion, and a point O61. Is one of the points near the boundary of the smooth part. When the optimum tilt drive value is set near the boundary of the smooth portion as at point O61 in FIG. 6, the tilt change corresponding to the radial tilt drive value ΔRo61 or more exceeds the smooth portion where the jitter value is almost constant and does not change. And
The jitter value greatly changes, that is, a slight tilt fluctuation greatly deteriorates the quality of the reproduced signal.

On the other hand, when the point O60 near the center of the smooth portion is set as the optimum tilt drive value, the jitter value exceeds the smooth portion where the jitter value hardly changes for the first time by a tilt change corresponding to the radial tilt drive value ΔRo60 or more. But,
ΔRo6 larger than the tilt change corresponding to ΔRo61
The jitter value is almost constant and does not change until a tilt change corresponding to zero. Therefore, when the optimum tilt drive value is set to ΔO60 which is the center of the smooth portion, the tilt margin can be increased. A method for realizing this will be described. The optimum tilt drive value search unit 1331 obtains a range of the tilt drive values in two directions that is equal to or less than the jitter value at which a high-quality reproduced signal can be obtained stably, and searches for the tilt drive values in the two directions that are the center of the range. I do.

More specifically, the 2 stored in the memory 132
From the tilt drive value in the direction and the jitter value, the maximum value rmax and the minimum value r of the tilt drive value in the radial direction are set at two tilt drive values in which the jitter value is equal to or less than a predetermined threshold value.
min and the maximum value tmax and the minimum value tmin of the tilt drive value in the tangential direction are obtained. It is the average of the maximum and minimum tilt drive values (rmax + rmi
n) / 2 and (tmax + tmin) / 2 as the optimum tilt drive values in the radial and tangential directions, respectively, and a DA converter 138
Output from 1. The optimum tilt drive value is a plane surrounded by an intersection of a characteristic in a three-dimensional space composed of a tilt drive value and a jitter value in substantially two directions and a plane where the jitter value is a predetermined value (threshold). The tilt drive value in two directions at the center of the rectangle circumscribing the figure is determined.

FIG. 6B shows the above-mentioned region and a rectangle circumscribing the above-mentioned region with respect to the radial and tangential tilt drive values. A point O62 is the center of the rectangle, and the radial and tangential tilt drive values are shown. Are (rmax + rmin) / 2 and (tmax + tmi, respectively)
n) / 2. According to the method described above, the point corresponding to the center O62 of the rectangle circumscribing the plane figure shown in FIG. The tilt drive value can be used, and a high-quality reproduced signal can be stably obtained with respect to a large tilt change.

The optimum tilt drive value search unit 1331
Is composed of a tilt drive value in two directions and a jitter value.
In the dimensional space, the center of gravity of the region of the tilt drive value in two directions that is equal to or less than the jitter value at which a high-quality reproduced signal can be obtained stably may be searched. Specifically, from the two-way tilt drive value and the jitter value stored in the memory 132, the number of combinations of the two-way tilt drive values for which the jitter value is equal to or less than a predetermined threshold value is n, and the radial of the combination is n. The tangential tilt drive value is defined as ri, ti (i = 1, 2, 2).
.., N), the average values “rave” and “tave” of the tilt drive values of all combinations are as follows: “rave = (r1 + r2 +... + Rn) / n” (13) “tave = (t1 + t2 +... + Tn) / n” (n) 14)

A tilt drive signal corresponding to the average values of the radial and tangential tilt drive values “rave” and “tave” as the optimum tilt drive values is converted to a DA converter 138.
Output from 1. At this time, the optimum tilt drive value is substantially 2
This corresponds to a tilt drive value in two directions at the center of gravity of a plane figure surrounded by an intersection of a characteristic in a three-dimensional space composed of a tilt drive value in the direction and a jitter value and a plane where the jitter value is a threshold.

FIG. 7 shows a plane figure on a plane where the above-mentioned jitter value becomes a threshold value for the radial and tangential drive values, a dotted line indicates a rectangle surrounding the plane figure, G7 indicates a center of gravity of the plane figure, O7 is the center of the rectangle surrounding the plane figure. Considering the tilt change in the radial direction at the center O7 of the rectangle circumscribing the plane figure shown in FIG. 7, the jitter value exceeds the threshold value due to the tilt change corresponding to the radial tilt drive value ΔRo7. In the center of gravity G7 of the plane figure, the jitter value exceeds the threshold value only at the tilt change corresponding to the radial tilt drive value ΔRg7, and the quality of the reproduced signal deteriorates.
That is, the tilt drive values in the two directions at the center of gravity G7 of the plane figure are greater than the center O7 of the rectangle circumscribing the plane figure.
A high-quality reproduced signal can be stably obtained with respect to a larger tilt change.

The optimum tilt drive value searching unit 1331 is
In the characteristics of the three-dimensional space composed of the tilt drive value and the jitter value in two directions, the center of gravity of the three-dimensional figure that is equal to or less than the jitter value at which a high-quality reproduced signal can be obtained stably may be searched. Specifically, from the two-way tilt drive value and the jitter value stored in the memory 132, the number of combinations of the two-way tilt drive values at which the jitter value is equal to or less than the predetermined threshold value JL is n, The radial and tangential tilt drive values and jitter values are defined as ri, ti, ji (i =
1, 2, ..., n). The value obtained by subtracting the jitter value ji of each combination from the threshold value JL is Δji = JL-ji
(I = 1, 2,..., N).

The weighted average values “rave” and “tave” based on Δji of the tilt drive values in all combinations are as follows: rave = (r1 × Δj1 + r2 × Δj2 +... t1 × Δj1 + t2 × Δj2 +... + tn × Δjn) / (Δj1 + Δj2 +... + Δjn) (16)

The tilt drive signal corresponding to the average values of the radial and tangential tilt drive values “rave” and “tave” as the optimum tilt drive values is converted to a DA converter 138.
Output from 1. At this time, the optimum tilt drive value is substantially 2
This corresponds to a tilt drive value in two directions at the center of gravity of a three-dimensional figure surrounded by a characteristic in a three-dimensional space composed of a tilt drive value in the direction and a jitter value and a plane where the jitter value is equal to the threshold value JL. By a method using a weighted average based on the jitter value, a characteristic in a three-dimensional space composed of a tilt driving value in two directions and a jitter value is surrounded by an intersection line with a plane where the jitter value is equal to a threshold value JL. The tilt drive value in the two directions at the center of gravity of the three-dimensional figure becomes smaller than the center of gravity of the three-dimensional figure to be obtained, and a high-quality reproduced signal can be obtained.

In the method described above, the tilt drive value at which the jitter value is minimized is searched for using the function approximation or the like in the case of the characteristic shown in FIG. Search for the center of Here, whether to use the above-described search method using the function approximation or the search method for finding the center or the center of gravity is selected based on the tilt drive value and the jitter value in two directions stored in the memory 132. A method of determining the characteristic shape determined by the above will be described with reference to the flow of FIG.

The optimum tilt drive value search unit 1331 obtains the minimum jitter value jmin from the combination of the tilt drive values in two directions and the jitter value stored in the memory 132 (S302). The jitter value jmin to which the predetermined value JS is added
+ JS The number n of combinations that are equal to or less than, in effect, the characteristics in a three-dimensional space composed of the tilt drive value and the jitter value in two directions and the area of the plane figure surrounded by the intersection line with the plane where the jitter value is jmin + JS. Find the equivalent (S
303). 2 when the number n of combinations is equal to or greater than a predetermined value
It is determined that the characteristic in the three-dimensional space composed of the tilt drive value in the direction and the jitter value is a pan-bottom characteristic having a smooth portion as shown in FIG. 4 (S304, S305, S3).
06).

Next, an optimum tilt drive value is searched for by a method based on the result of the characteristic shape determination. In the characteristic shape determination, when it is determined that the characteristic is a pan-bottom characteristic, the jitter value characteristic in the center of the smooth portion of the characteristic in the three-dimensional space is determined.
A tilt drive value in the direction is searched for (S308). If it is determined that the characteristic is not pan-shaped, a tilt drive value in the two directions that minimizes the jitter value is searched for (S307). By setting the tilt drive value searched for in each case as the optimum tilt drive value, even if the characteristics of the optical disc 101 are not limited to those in FIG. A high-quality reproduction signal can be stably obtained.

The method for determining the characteristic shape is described in the memory 13.
The minimum jitter value jmin from the combination of the tilt drive value and the jitter value in the two directions stored in 2 is set to a predetermined value JS.
, The maximum number rmax and the minimum value rmin of the tilt drive value in the radial direction and the maximum value tmax and the minimum value tmin of the tilt drive value in the tangential direction among the combinations are obtained. The product Sa of the difference between the maximum and the minimum of the tilt drive value in each of the two directions is obtained.

Sa = (rmax−rmin) × (tmax−tmin) (17) The number n of combinations is substantially the same as the characteristic in a three-dimensional space composed of a tilt drive value and a jitter value in two directions. The product Sa corresponds to an area of a plane figure surrounded by an intersection with a plane having a jitter value of jmin + JS, and the product Sa corresponds to a rectangle circumscribing the plane figure. If the ratio between the number of the obtained combinations and the product is equal to or greater than a predetermined value, a method of determining that the characteristics are pot-bottom-like may be employed.

The method for determining the characteristic shape is described in the memory 13.
The minimum jitter value jmin from the combination of the tilt drive value and the jitter value in the two directions stored in 2 is set to a predetermined value JS.
And the number of combinations that are equal to or less than the jitter value jmin + JS, and the jitter value ji (i =
The sum Ssum of the differences Δji between (1, 2,..., N) and jmin + JS is determined.

Δji = jmin + JS−ji (18) Ssum = Δj1 + Δj2 +... + Δjn (19) The number n of combinations is substantially composed of a tilt drive value and a jitter value in two directions in the former case. It corresponds to the area of a plane figure surrounded by the intersection of the characteristic in the dimensional space and the plane where the jitter value is jmin + JS, and the sum Ssum of the difference Δji between the jitter values is composed of the tilt drive value and the jitter value in two directions. The characteristic and the jitter value in the three-dimensional space are jmin + J
This corresponds to the volume of a three-dimensional figure surrounded by a plane serving as S.
The sum S of the number n of combinations obtained and the difference Δji between the jitter values
If the ratio with the sum is equal to or more than a predetermined value, a method of determining that the characteristic is a pot bottom shape may be used.

[0071]

As described above, according to the present invention, since the search for the tilt drive values in two directions is performed simultaneously, there is no need to perform the correction repeatedly without being affected by the tilt drive values in each direction.
High-speed and high-precision two-way tilt correction can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disk device according to an embodiment of the present invention.

FIG. 2 is a flowchart of searching for an optimum tilt drive value according to the embodiment of the present invention;

FIG. 3 is a three-dimensional spatial characteristic diagram showing a change in a jitter value with respect to a tilt drive value in two directions for explaining the embodiment of the present invention;

FIG. 4 is a three-dimensional spatial characteristic diagram showing a change in a jitter value with respect to a tilt drive value in two directions of a pan bottom for explaining the embodiment of the present invention;

FIG. 5 is a three-dimensional spatial characteristic diagram showing a change in a jitter value with respect to a tilt drive value in two directions having a biased shape for explaining the embodiment of the present invention;

FIG. 6 is a characteristic diagram showing a change in a jitter value with respect to a tilt drive value in two directions for explaining the embodiment of the present invention;

FIG. 7 is a characteristic diagram showing a change in a jitter value with respect to a tilt drive value in two directions for explaining the embodiment of the present invention;

FIG. 8 is a flowchart of an optimum tilt drive value search based on characteristic shape determination for describing an embodiment of the present invention.

FIG. 9 is a characteristic diagram showing a change in a jitter value with respect to a tilt control target value in two directions for explaining a conventional technique.

FIG. 10 is a characteristic diagram showing a change in a jitter value dependent on a tilt control target value in two directions for explaining a conventional technique.

FIG. 11 is a block diagram showing a configuration of an optical disk device according to a conventional technique.

[Explanation of symbols]

 101 Disk 111 Optical Pickup 112 Light Beam 121 Binarization Circuit 122 Jitter Detection Circuit 130 DSP (Digital Signal Processor) 131 Tilt Detection Signal Measuring Unit 1311 Tilt Detection Signal Measuring Unit (2 Directions) 132 Memory 133 Optimal Tilt Correction Amount Searching Unit 1331 Optimal tilt drive value search unit 135 AD converter (jitter signal input) 138 DA converter (tilt control target signal output) 1381 DA converter (tilt drive signal output) 141 Tilt mechanism 1411 Tilt mechanism (two directions) 142 Tilt sensor 143 Tilt control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Kishimoto 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5D118 AA13 BA01 CA08 CD04 CD05 CD08

Claims (16)

[Claims] 1. A tilt error signal that changes in accordance with two tilt angles generated between an information recording surface of a record carrier and an optical axis of a light beam is generated. By changing the tilt angle in two directions between the axis and
A tilt correction method for an optical disc, characterized in that an optimum correction amount is searched for and determined based on a characteristic in a three-dimensional space constituted by a tilt error signal and a correction amount for a tilt angle in two directions. 2. An apparatus for optically recording and reproducing information on and from a record carrier, wherein the signal changes in accordance with a tilt angle in two directions generated between an information recording surface of the record carrier and an optical axis of a light beam. A tilt error signal generating means for generating the tilt error signal, a tilt correcting means for correcting a tilt angle in two directions generated between the information recording surface of the record carrier and the optical axis of the light beam, and an output of the tilt error signal generating means. An optimum tilt correction amount searching means for searching for and determining an optimum correction amount based on a characteristic in a three-dimensional space constituted by a tilt error signal and a correction amount for a tilt angle in two directions for driving the tilt correction means. Optical disk device. 3. The tilt error signal generating means includes light detecting means for detecting reflected light of a light beam from an information recording surface of a record carrier, and outputting a jitter of a signal output from the light detecting means. 3. The optical disk device according to claim 2, wherein: 4. The optical disc apparatus according to claim 2, wherein said tilt correcting means relatively displaces the inclination between the optical axis of the light beam and the information recording surface of the record carrier. 5. The optimum tilt correction amount searching means changes a correction amount of the tilt correction means with respect to two tilt angles, measures a tilt error signal output from the tilt error signal generation means, and calculates a tilt error signal. Function approximating means for approximating the relationship between the signal and the correction amount for the two directions of tilt angle of the tilt correcting means to a function, based on the function approximated by the function approximating means; 3. A search for a correction amount.
An optical disk device as described in the above. 6. The method according to claim 5, wherein said function approximating means approximates to a second-order polynomial by a least squares calculation.
An optical disk device as described in the above. 7. The function approximation means includes storage means for storing a singular value decomposition matrix calculated from correction amounts of the tilt correction means with respect to two tilt angles, based on a singular value decomposition matrix stored in advance. 7. The optical disk device according to claim 5, wherein an approximate function is obtained. 8. The optimum tilt correction amount searching means changes a correction amount of the tilt correction means with respect to two tilt angles, measures a tilt error signal output from the tilt error signal generating means, and calculates a tilt error signal. 3. The optical disc apparatus according to claim 2, wherein the center of the range of the amount of correction for the tilt angle in the two directions of the tilt correction means at which the signal becomes substantially minimum or substantially maximum is the optimum correction amount. 9. The three-dimensional space defined by the optimum tilt correction amount searching means, comprising a correction amount for the tilt angle in two directions of the tilt correcting means and a tilt error signal output from the tilt error signal generating means. The tilt error signal characteristic obtained by changing the amount of tilt angle correction in the two directions by the tilt correction means and measuring the tilt error signal and the center of gravity of the plane figure surrounded by the intersection of the plane having the tilt error signal as a predetermined value. 9. The optical disk device according to claim 8, wherein the correction amount for the two tilt angles is an optimum correction amount. 10. The three-dimensional space defined by the optimum tilt correction amount searching means, comprising a correction amount for the tilt angle in two directions of the tilt correcting means and a tilt error signal output from the tilt error signal generating means. A tilt error signal characteristic obtained by measuring a tilt error signal by changing a correction amount for the tilt angle in the two directions of the tilt correction means, and a center of gravity of the two-dimensional object surrounded by a plane having the tilt error signal as a predetermined value. 9. The optical disk device according to claim 8, wherein the correction amount for the tilt angle is an optimum correction amount. 11. The three-dimensional space defined by the optimum tilt correction amount searching means, comprising a correction amount for the tilt angle in two directions of the tilt correcting means and a tilt error signal output from the tilt error signal generating means. A characteristic shape determining unit configured to determine a shape of a tilt error signal characteristic obtained by measuring a tilt error signal by changing a correction amount of the tilt correcting unit with respect to a tilt angle in two directions, based on the determination by the characteristic shape determining unit. 3. The optical disk device according to claim 2, wherein a correction amount for a tilt angle in two directions is searched. 12. The three-dimensional space defined by the characteristic shape determination means, comprising a correction amount for the tilt angle in two directions of the tilt correction means and a tilt error signal output from the tilt error signal generation means. The tilt error signal is measured by changing the amount of correction for the tilt angle in two directions by the tilt correction means, and the tilt error signal is measured based on the area of the plane figure surrounded by the intersection line with the plane having the tilt error signal as a predetermined value. 12. The optical disk device according to claim 11, wherein the shape of the tilt error signal characteristic is determined. 13. The three-dimensional space defined by the characteristic shape determination means, comprising a correction amount for the tilt angle in two directions of the tilt correction means and a tilt error signal output from the tilt error signal generation means. The area and plane figure of the plane figure surrounded by the intersection of the tilt error signal characteristic obtained by measuring the tilt error signal by changing the correction amount for the tilt angle in two directions by the tilt correction means and the plane having the tilt error signal as a predetermined value. 12. The optical disk device according to claim 11, wherein the shape of the tilt error signal characteristic is determined based on a ratio of an area of a rectangle circumscribing the tilt angle. 14. The three-dimensional space defined by the characteristic shape determination means, comprising a correction amount for the tilt angle in two directions of the tilt correction means and a tilt error signal output from the tilt error signal generation means. The tilt error signal characteristic obtained by measuring the tilt error signal by changing the amount of correction for the tilt angle in two directions by the tilt correction means, and the area and tilt error of the plane figure surrounded by the intersection of the plane having the tilt error signal and the predetermined value. 12. The tilt error signal characteristic shape is determined based on a ratio between a signal characteristic and a volume of a solid surrounded by a surface having a predetermined value of the tilt error signal.
An optical disk device as described in the above. 15. An optimum tilt correction amount search means for measuring a tilt error signal output from the tilt error signal generation means by changing a correction amount of the tilt correction means with respect to a tilt angle in two directions. A function approximating unit that approximates a relationship between a signal and a correction amount for the tilt angle in two directions of the tilt correcting unit to a function, based on the function approximated by the function approximating unit according to the determination by the characteristic shape determining unit 12. The method according to claim 11, wherein an optimal correction amount for an optimal tilt angle in two directions is searched.
5. The optical disk device according to any one of 4. 16. The optimum tilt correction amount searching means, wherein the tilt angle in two directions of the tilt correcting means, wherein the output of the tilt error signal generating means becomes substantially minimum or substantially maximum according to the determination by the characteristic shape determining means. 15. The optical disk device according to claim 11, wherein a center of a range of the correction amount for the optical disk is an optimum correction amount.